Preparation of substituted glutaric acid esters



Patented Sept. 12, 1950 I UNITED STAT ES. PATENT}; OFFICE] 1 2.52m g v ';i-

PREPARATION OF SUBSTITUTED GLU'IAItIC 1 1' I BSY' 1 IT William -F. Gresham, Wilmingtom-DeL, assignor to E. I. du Pont de Nemours &0ompany,;Wil

ming'ton, Del., a corporation of Delaware: "1

ApplicationNovember 1, 19 4 7," Serial No. 783,627

No Drawing.

'Claims. (o1. act-485) f This invention relates to "a process for the preparation of dialkyl esters or alpha-methylene glutaric acid, and more particularly to the preparation of such esters from alkylfbeta alkoxypropionates. I w r It is known that the alkyl acrylates can be prepared from the beta-alkoxypropionic acid esters by reacting these esters using acids, or alkali metal alkoxides as catalysts. In'these known reactions, however, the free alcohol formed and/or used as a solvent is distilled off as the reaction proceeds. (N. M. Bortnick, U. S. Patent 2,393,737.) Similarly, substituted products are prepared by conducting a reaction of the alkyl beta-alkoxy carboxylic acids in the pres ence of an alcohol boiling higher than the alco-f hol split off the ester during the reaction. (Seeger Patent U. .8. 2,393,000.) In these reactions the removal of alcohols formed during the reaction precludes the possibility of converting the ester reacted to glutarate esters.

An object of the present invention is to provide a process for the preparation of new com: positions of matter. A'furtherobject is to provide" a process for the preparation of dialkyl esters of alpha-substituted glutaric' acids from alkyl beta-alkoxypropionates in the presence of a condensation catalyst. Another object is to providea process for the polymerization of dialkyl esters of alpha-methylene glutaric acid arevseparated bydistillatlon, and the'glutarate" then recovered from the residue by vacuum distillation.

Generally, .thereactlon may beillustrated by the equation: v i 1 znoemomooon,---2RoH+R,ooocoH.omo00R.

wherein R and R1 are similar or dissimilar alkyl groups such as methyl, ethyl, normal and iso-x propyl, normal and isobutyl, and'higher alkyl;

groups; organ aryl group, such as phenyl or;

accord with this equation:

and, likewise, the polymers thus obtained. Other objects 'and advantages of the i nvention will I hereinafter appear.

The monomeric esters oi. "alpha-methylene glutaric acid are prepared in' accord with the invention by subjecting an alkyl beta-alkoxy-' propionate to a sufficiently high temperature, generally at-about the b'oiling'point of the ester, to split off an alcohol, the reaction being effected in the presence of a basic catalyst and without removing by distillation or otherwise the alcohol or other low boiling products of: the reaction. If the, low boiling compounds are taken off dur-' ing the reaction, the formation of glutaric acid esters is suppressed. Moreover, it is recom-; mended that no solvent such as an alcohol be added with the catalyst or tothe reaction for,

although alcohols are formedduring the reaction-, -an excess over and above the. formed alcohol lowers appreciablythe rate: of reaction.

there is also obtained, probablyas an. intermediate, some dimethyl alpha-methoxymethyl-e glutarate, which is believed to be formed in.

( CH|OCHCH|COOCH9 CHaQCHaCHzCOOCHs 011.011 onioo'oonon oin'oooon. B. Two moles'of methyl-methoxypropionate un-iu dergoes condensation with one moleof methanoL. splitting ofi to give methyl-alpha-methoxymethyl glutarate which in turn partially decom poses to form dimethyl-alpha-methylene. glutarate as indicated by equation: 7,

4) H moooonomomoooon. 011.0011.

" cmoir+ ornooooomomoo'o'om The-reaction conducted at a temperaturebetween '75? and 150 C. and preferably-between 780 and 110 C. Pressures do not appear to mastantially constantfor from V to 8 hoursdepending upon catalystgconcentration., There action mixture is then neutralized, by-products terially efiect the course oi the reaction, although reduced, superatmospheric or normalpressures may beemployedtii desired. 1,

The, examples illustrate preferredl"'embodi mentsoi the invention in which parts-are by weight unless otherwise indicated.

Example 1;Methyl-beta-methoxypropionate containing 1% hydroquinone and 1% sodium methoxide as the catalyst was heated in a flask, provided with a reflux condenser without a vapor take-off, with stirring to a temperature between 100 and 105 C. An exothermic reaction occurred, boiling commenced, andthe temperature fell to between 85 'and 90 C. The mam-was permitted to proceed for approximately /4 hour.

Glacial acetic acid was then added to neutralize" the catalyst. The resulting mixture was subjected to distillation, methyhalcoholfimethyl' acrylate, and methoxy propionate distilling over leaving dimethyl alpha-methylene glutarate and dimethyl alpha-methoxymethyl. glutarate, which were separated by vacuum fractional distillation in a conversion of approximately 15%, and a yield between 85 and 90%.

1 I likewise be conducted with advantage by a con- The compounds have these properties: Di-

methyl alpha-methylene glutarate; B. P. 73'/2.5'

mm., 12 1,4436; saponification number: found 646 and 661; calculated 6501mm KOH/g... sample;.

Dimethyl; alpha-methoxymethylglutarate; B. P. lid-.lQi/l. mm. 11. 1..133'0;saponification-numberz calculated, 550; found, 5&0; methoxyl::.calculatecl,..

methoxyl found 0.5%; calculated 15.2%; found 13.2%.

Example 2.-A flask similar to that used in Example 1 was charged with 40 parts of methyl beta-methoxypropionate and one part of sodium methoxide. The charge was heated for hour at a temperature between 1.00 and.135 .C; and

then heated under reflux without vapor take-ofi for one hour. The pressure was-reduced from2 to mm. and 3.3 parts of the product recovered 'at 80 to 85 C. The residue was'resinous.

A sample of the 80 to 85 C.'fraction was'hydrolyzed with hydrochloric acid. On cooling,

crystalline alpha-methylene glutaric acids separated. After washing and drying, it had M. P. 128-9 C.

Example 3.Methyl beta-methoxypropionate, 40 parts, and sodium methoxide, 0.25-part, were mixed with 0.1 part of hydroquinone in a glass flask. The resulting mixture was warmed on a waterbath for one hour under a nitrogen blanket.

The resulting mixture was then allowed to stand over night and wasthen diluted with ether and washed 3 times with water.- 4.5 parts of dimethyl alpha-methylene-glutarate was obtained as described in Example 2 which constituted a yield of 75%.

Example 4.-Methyl beta-methoxypropionate 58.5 parts, hydroquinone 0.3 part, and sodium methoxide 0.5 part were charged in a flask and heated to 120 C. for 15 minutes. No reaction appeared to take place during-this time. A few drops of methanol did-not initiate the reactionnor did the addition of 0.2 part more of sodium methoxide. The addition of 0.2 additional part of sodium methoxide makinga total of 0.9 part caused a vigorous reaction. The mixture was refluxed without vapor take-off for 15 minutes and sodium was added in pieces A vigorous reaction tinuous process. Such a process may be carried out-by passing, at controlled rate, the alkyl betaalkoxypropionate' containing the catalyst into a tubular reaction zone of considerable length wherein the temperature of the reaction is controlled by any suitable heating means. The reaction mixture as it issues from the converter is neutralized and the resulting neutral or slightly acidic mixture subjected to distillation for, the recovery of the esters; Methyl acrylate and methyl alpha-methoxymethyl glutarate produced as byproduct may be recycled to the reaction mixture for conversion to methoxypropionate and methylene lutarate.

The reaction has been found to be a general one for the treatment of esters of beta-alkoxypropionic acid and especially for the treatment of the lower alkyl estergsueh as the methyl, ethyl, normal and isopropyl, normal and isobutyl esters of the beta-lower-alkoxy: e. g., beta-methoxy, beta-ethoxy, and beta-propoxypropionates.

In addition to the catalysts described in the examples, other alkali metal and alkaline earth metal alkoxides generally may be employed as well as their oxides, hydroxides, and the quaternary ammonium hydroxides and organic amines, those soluble in the ester treated being preferred.

Inasmuch as the products of the reaction are polymerizable, it is advantageous to use along with the catalyst a suitable polymerization inhibitor, such, for example, as hydroquinone, pyrogallol, elemental sulfur, or other well known polymerization inhibitors which are capable of inhibitlng the polymerization of compounds containing an unsaturated olefinic bond.

The alpha-methylene glutarates produced in accord with this invention are polymerizable to colorless, glass-like,. tough, solid polymers by heating the ester. .in the presence of a suitable polymerizingcatalyst, such, for example, as organic compounds known as free -radical formers.

By this, ,I mean such catalysts as an azo compolymerization catalyst.

The polymerization may take place spontaneously but is preferably controlled-by heating the unsaturated alpha-methylene glutarates and like esters to a temperature between 70 C. to 250 C.

Example 7.-To about 5 parts of dimethyl alpha-methylene glutarate was added 0.05 part of dibenzoyl peroxide. The mixture was heated on a steam bath for six hours during which time the liquid increased in viscosity and finally produced a colorless, hard, organic glass.

The dialkyl alpha-methylene glutarates have many valuable uses. In their monomeric form; they may be employed effectively as solvents and plasticizers, and in the latter use they may be dissolved in the resin to be plasticized and polymerized in situ or not as desired. In their polymeric form they may be used in the preparation of molding powders for injection molding,"

for example. The alpha-alkoxymethyl-substituted. glutarates are all likewise suitable as solvents and plasticizers and for various other'uses.

I claim: V 1. A process for the preparation of alpha-substituted glutaric acid esters which comprises heating a mixture of an alkyl beta-alkoxypropionate, a polymerization inhibitor and an alkaline condensation catalyst, thereby converting the ester to an alpha-substituted glutaric acid ence of the alcohol as it is split ofi the alkyl beta alkoxypropionate during the conversion.

2. The process of claim I conducted at a temperature between and 0.

3. A process-for the preparation of dimethyl alpha-methylene glutarate which comprises heating a mixture of methyl beta-methoxypropionate, a polymerization inhibitor, and an alkaline condensation catalyst, thereby converting the methyl beta-methoxypropionate to dimethyl alpha-methylene"glutarate and conducting the conversion in the presence of the methanol as it is split off the methyl beta-methoxypropionate during its conversion.

4. The processor claim 3 in which an alkali metal alkoxide is employed as the catalyst.

5. The process of claim 3 conducted at a temperature betwee'ri-Fiand C. and in the presence of sodium methoxide as the catalyst.

' WILLIAMF. GRESHAM.

REF RENCES CITED The following references are of record in the file of this patent:

'UNITED; STATES PATENTS Number Name Date 2,313,501 Bachman et al Mar. 9, 1943 2,341,663 Schulz Feb. 15, 1944 2,433,616 Marple et a1. Dec. 30, 1947 OTHER REFERENCES Beilstein, Handbuch der organischen Chemie,

ester and conducting the conversion in the pres- 30 4th Page 775 (1920 page 657 Goss, J. Chem. Soc. London, vol. 127, pages 

1. A PROCESS FOR THE PREPARATION OF ALPHA-SUBSTITUTED GLUTARIC ACID ESTERS WHICH COMPRISES HEATING A MIXTURE OF AN ALKYL BETA-ALKOXYPROPIONATE, A POLYMERIZATION INHIBITOR AND AN ALKALINE CONDENSATION CATALYST, THEREBY CONVERTING THE ESTER TO AN ALPHA-SUBSTITUTED GLUTARIC ACID ESTER AND CONDUCTING THE CONVERSION IN THE PRESENCE OF THE ALCOHOL AS IT IS SPLIT OFF THE ALKYL BETAALKOXYPROPIONATE DURING THE CONVERSION. 